: An epithelium provides a barrier to protect and compartmentalize organs from hazardous external environments. Epithelial barrier disruption causes inflammation; chronic barrier disruption if unchecked can lead to malignant cell transformation, ultimately producing cancer. Arachidonic acid (AA) metabolites, i.e. eicosanoids, are produced in response to epithelial barrier disruption. In vertebrates, eicosanoids are essential lipid mediators of epithelial barrier maintenance, inflammation, cellular growth and proliferation. Emerging evidence suggests eicosanoids may play a central role in cellular transformation. Cyclooxygenases (COX) convert AA into proliferative and trophic eicosanoids, the prostaglandins, which are mediators of tumorigenesis. Lipoxygenases, on the other hand, convert AA into pro- and anti-inflammatory eicosanoids, such as leukotrienes and lipoxins. Suppression of the trophic class of eicosanoids, via non-steroidal anti- inflammatory drugs (NSAIDs), protects against cancer. There is a critical need to test how eicosanoid mediated epithelial barrier loss and inflammation promote cellular transformation. One of the least studied, yet most highly expressed epidermal lipoxygenases, Alox12, is essential for epithelial barrier maintenance throughout phyla. Mutations in human ALOX12 are associated with congenital ichthyosiform erythroderma, characterized by loss of epidermal barrier function, over proliferation, and inflamed skin. Intriguingly, ALOX12 is co-deleted with p53 in many human tumors. Thus, understanding its cancer-related functions is highly relevant. Given the above rationale, I hypothesize that the eicosanoid-producing enzyme, Alox12, acts as a tumor suppressor in two non-mutually exclusive ways: (1) through its function in epithelial barrier maintenance, preventing epithelial inflammation, and (2) by balancing arachidonic acid metabolism to inhibit cellular transformation. Transparent zebrafish larvae are especially well suited to test the role of eicosanoid-mediated epithelial barrier maintenance, inflammatory, and cellular transformation by live imaging. I find loss or Alox12, with CRISPR gene editing or morpholino mediated knockdown, generates lesions of hyperplasia within the zebrafish epithelium. This phenotype is associated with leukocyte retention, and up regulation of inflammatory genes, indicative of a tumor-promoting tissue microenvironment. I aim to test (1) the consequences of Alox12 loss on epithelial barrier maintenance and inflammation, (2) how Alox12 loss affects epithelial eicosanoid metabolism in human and zebrafish cells, (3) whether Alox12 loss promotes cell transformation and tumor formation. Through live imaging and lipidomic analysis in zebrafish and cell culture models, I seek to dissect the fundamental mechanisms of eicosanoid-induced epithelial barrier maintenance, inflammation, and malignant cellular transformation that may be exploited for therapeutic benefit in the future.